This invention relates to a combined soil reinforcement and drainage grid and in particular relates to a process of making the same.
Soil reinforcement grids or networks of synthetic polymeric material are known for the stabilisation of soil in construction sites and the like. It has been proposed to incorporate a drainage means within such a grid to aid drainage of the soil for quickly draining rain water and accumulated underground water thereby alleviating hydraulic pressure exerted on the ground, increasing ground stability and preventing earth movement from occurring on a construction site.
The present invention seeks to provide a simple and convenient process for producing such grids of polymeric material in an economical manner.
According to the present invention there is provided a method of producing a drainage grid or network comprising a number of interlocked strips which comprises providing a warp direction a plurality of strips having a channel or channels formed longitudinally therein, feeding such strips into a bonding zone wherein a filter material is bonded over the channel or channels, subsequently providing strips of polymeric material transverse to the warp strips and bonding them thereto to form the weft of the network and thereafter collecting the network or grid so produced.
The collection is conveniently carried out by winding the so-produced network onto a roll.
When bonding the weft strips to the warp strips carrying the filter material and channels, care should be taken to avoid crushing the channels and/or bonding the filter material down into the base of the channels. Accordingly, it is preferred the weft is bonded to the warp only in those areas adjacent the channel or channels.
The warp and weft may be produced from yarn reinforced polymeric webbing which is heat bonded to give a mesh. It has been found that polyolefin materials, particularly polyethylene, are suitable. Where reinforcing is provided this may be in the form of reinforcing polyester yarns and are preferably inserted in the longitudinal direction in bundles.
The filter fabric may also be a thermoplastic material and may be heat bonded, needle punched or woven. The filter fabric is adhered to, preferably by hot bonding, the warp using an elevated temperature and pressure.
The process is preferably carried out in a machine which may advantageously be operated in a step-wise manner so that each warp strip is bonded to a length of filter fabric and then the machine indexed forward for the next stage. The length of step chosen is preferably that between adjacent wefts so that indexing the strips forward one unit places the warp in position for both the next filter bonding stage as well as the next weft attachment stage.
The bonding of the filter fabric to the warp is a critical part of the invention. The bonding unit preferably hot bonds the filter fabric to the surface of the warp to provide a satisfactory continuous bond without destroying the structure of the filter fabric. This is done by ensuring that the combination of bonding temperature, bonding time, bonding pressure and bonding anvil material are controlled. The dominating parameter is bonding pressure. By using a pressure, for example, in the range 0.3 to 0.7 N/mm2 the temperature can be reduced so as not to melt or shrink the filter fabric, and the bonding time can be controlled to give a satisfactory bond. The uniformity of the bond is determined by the hardness of the bonding anvil. It has been found that a synthetic rubber material with a shore hardness of 50xc2x0 to 70xc2x0 gives satisfactory results which compensate for variations in web and filter fabric thickness.
The invention will be described further, by way of example, with reference to the accompany drawings, in which: